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NASA NTRS1985

An experiment to measure the energy spectrum of cosmic ray antiprotons from 100 to 1000 MeV

Production models were developed and the confirmation of each one had significant astrophysical impact. These include radical modifications of propagation models, cosmic ray antiprotons injection from neighboring domains of antimatter, p production by evaporating primordial black holes, and cosmic ray p's as annihilation products of supersymmetry particles that might make up the dark dynamical mass of the Galaxy. It is that p's originating from supersymmetric parents might have distinct spectral features that would survive solar modulation; in one model, higgsino annihilation proceeds through the bb quark-antiquark channel, producing a spectral bump at approx. 0.3 GeV in the p spectrum.

Salamon, M. H.↗

NASA NTRS1981

Measurement of the 0.511 MeV gamma ray line from the Galactic Center

The detection of the 0.511 MeV electron positron annihilation line coming from the Galactic Center to provide the means to estimate the rate of positron production and to test some theoretical sources of positrons is addressed. The results of the measurements of the 0.511 MeV line flux made with a gamma ray experiment on board a stratospheric balloon are presented. The detector field of view looked at the galactic longitude range -31 deg l(II) +41 deg. The observed flux is 0.0067 (+ or - 0.0005) photons 1/cm(2)5 which is in very good agreement with the expected flux when assuming that the Galactic Center is a line source emitting uniformly.

Jardim, J. O. D.↗

NASA NTRS1973

Gamma ray and neutron measurements and their relation to the solar flare problem.

In order to interpret recent observations of solar gamma ray lines from OSO-7, we consider the possible nuclear reactions which can occur and assess their relative importance in the solar environment. This analysis shows that about 3 times 10 to the 32nd power protons (energy greater than 30 MeV) must have been produced during the initial phase of the flare on Aug. 4, 1972. The ability to determine the temperature in the solar region where the positrons annihilate has been estimated from the 0.51 MeV line width, giving a temperature there of less than 7 million deg K. The major conclusions from these observations are discussed and some outstanding problems are mentioned. Finally, requirements for the next generation of solar gamma ray and neutron experiments are discussed.

Chupp, E. L.↗

NASA NTRS1986

A flare-induced cascade model of gamma-ray bursts

An analytical model is developed for the source of gamma ray bursts as a stellar flare in the magnetosphere of a neutron star. It is suggested that the loss of energy through synchrotron radiation experienced by electrons moving through a sufficiently strong magnetic field at a large pitch angle may not be regained. Instead, pulsar theory is applied to show that the acceleration of electrons in an electric field parallel to the magnetic field will rapidly be inhibited by curvature radiation as the loop experiences a reconnection. It is shown that electrons passing through a curvature with a radius of one million with an electric field strength of 10 billion e.s.u. will emit photons with energies of up to 10 to the 12.6 eV by curvature radiation. The photons, gamma rays, would annihilate in the magnetosphere, which they cannot escape. The resulting cascade of electron-positron particles would eventually produce photons of sufficiently low energy to escape. Upper and low bounds are estimated for the resulting emission spectrum, which would vary according to the magnetic field geometry. The model explains the observed 511 keV annihilation line and the optical radiation which at times accompanies gamma-ray bursts.

Sturrock, P. A.↗

NASA NTRS2016

Heavy Right-Handed Neutrino Dark Matter and PeV Neutrinos at IceCube

We discuss a simple non-supersymmetric model based on the electroweak gauge group SU(2) (sub L) times SU(2) prime times U(1) (Sub B-L) where the lightest of the right-handed neutrinos, which are part of the leptonic doublet of SU(2) prime, play the role of a long-lived unstable dark matter with mass in the multi-Peta-electronvolt range. We use a resonant s-channel annihilation to obtain the correct thermal relic density and relax the unitarity bound on dark matter mass. In this model, there exists a 3-body dark matter decay mode producing tau leptons and neutrinos, which could be the source for the Peta-electronvolt cascade events observed in the IceCube experiment. The model can be tested with more precise flavor information of the highest-energy neutrino events in future data.

Bhupal Dev, P. S.↗

NASA NTRS1980

Positron annihilation studies of moisture in graphite-reinforced composites

The positron lifetime technique of monitoring absorbed moisture is applied to several composites, including graphite/polymides which are candidates for high-temperature (over 260 C) applications. The experimental setup is a conventional fast-slow coincidence system wherein the positron lifetime is measured with respect to a reference time determined by the detection of a nuclear gamma ray emitted simultaneously with the positron. From the experiments, a rate of change of positron mean lifetime per unit mass of water can be determined for each type of specimen. Positron lifetime spectra are presented for a graphite/polyimide composite and for a pure polyimide.

Singh, J. J.↗

NASA NTRS1995

Search for Compton-backscattered annihilation radiation from the galactic center with the OSSE

An emission feature near 170 keV, interpreted as Compton-backscattered 511 keV positron-annihilation radiation, has been reported twice by balloon-borne germanium spectrometers from within approximately 15 deg of the Galactic center (Leventhal, MacCallum, & Stang 1978; Smith et al. 1993). Upper limits on this feature set by HEAO 3 (Mahoney, Ling, & Wheaton 1993) and other instruments indicate that it must be transient. We have searched data from the Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory (CGRO) for this feature, using daily spectral accumulations from all pointings near the Galactic center up to 1993 August, and covering most of the region viewed by the balloon instruments. We find no evidence for backscatter emission. Under the hypothesis that the source is 1E 1740.7-2942, the OSSE data set (186 days) disagrees with the balloon measurements with 99.3% confidence. The average daily 3 sigma OSSE upper limit on bakscatter flux from 1E 1740.7-2942 is 6.8 x 10(exp -4) photons/sq cm/s, compared to the 1.3 x 10(exp -3) photons/sq cm reported by the balloon observations. We also saw no evidence in 186 days for linelike emission from the point source EXS 1737.9-2952 recently discovered by Grindlay, Covault, & Manandhar (1993). This source exhibited bright emission from 83-111 keV, which has been interpreted as doubly backscattered 511 keV radiation. The average daily 3 sigma upper limit from OSSE for this line is 9.8 x 10(exp -4) photons/sq cm/s, or approximately 8% of the reported flux.

Smith, D. M.↗

NASA NTRS1995

OSSE observations of 1E 1740.7-2942 in 1992 September

We present data on the galactic X-ray source 1E 1740.7-2942 from the Oriented Scintillation Spectrometer Experiment (OSSE) on board NASA's Compton Gamma Ray Observatory (CGRO). Episodes of increased low-energy gamma radiation have been reported from this source, including 1-day events in 1990 October and 1992 September. These events, of intensity 7 x 10(exp -3) and 4 x 10(exp -3) photons/sq cm/s, respectively, have been interpreted as broadened and redshifted positron annihilation radiation. OSSE conducted observations of the Galactic Center region during a 21-day interval from 1992 September 17 thru 1992 October 8. This includes the time of increased 200-450 keV emission from 1E 1740.7-2942 reported by SIGMA. The OSSE observations do not confirm this event. For the specific outburst recorded by SIGMA, 1992 Sep. 19.42-20.58 (UT), OSSE data provide an upper limit (3 sigma) of 2.4 x 10(exp -3) photons/sq cm/s.

Jung, G. V.↗

NASA NTRS2003

RF Manipulation and Detection of Protons in the High Performance Antiproton Trap (HiPAT)

The significant energy density of matter-antimatter annihilation is attractive to the designers of future space propulsion systems, with the potential to offer a highly compact source of power. Many propulsion concepts exist that could take advantage of matter-antimatter reactions, and current antiproton production rates are sufficient to support basic proof-of-principle evaluation of technology associated with antimatter-derived propulsion. One enabling technology for such experiments is portable storage of low energy antiprotons, allowing antiprotons to be trapped, stored, and transported for use at an experimental facility.

Martin, James J.↗

NASA NTRS1988

Recent observations of cosmic ray antiprotons and a critical assessment of the theories of their origin

The models proposed to explain the observed spectrum of cosmic ray antiprotons are reexamined in light of recent results from balloon-borne experiments. It is found that the prediction of modified closed galaxy model fits the observed data very well. Models in which secondary antiprotons are produced in the sources, could be made consistent with the data provided the secondary particles do not suffer considerable adiabatic deceleration. It has been shown that there cannot be any significant contribution to the observed antiprotons, from the evaporation of mini black holes or from the annihilation of dark matter like photinos. The role of extragalactic cosmic rays has been examined critically in the context of the recent data, and they are not the source of cosmic ray antiprotons. However, determination of the energy spectrum of antiprotons at least up to a few tens of GeV would be valuable to provide information on the possible existence of supersymmetric particles and on the modulation of extragalactic cosmic rays while entering the Galaxy.

Stephens, S. A.↗

NASA NTRS1976

Measurement of the positron-electron reaction which produces a gamma ray pair in the region psi/3684/

An experiment was conducted to measure gamma ray pairs produced in the electron-positron reaction in the region of psi(3684) resonance. The apparatus consisted of two identical spectrometers mounted in a collinear configuration about the beam interaction region. Graphs are presented for the coplanarity angle between reconstructed gamma ray directions, for the scattering and energy deposition of gamma rays in the two crystals used, and for the observed rate of annihilation reactions as a function of center of mass energy.

Hughes, E. B.↗

NASA NTRS1997

The great annihilator 1E 1740.7-2942: Molecular cloud connection and coronal structure

Using (12)CO and (13)CO observations, column density maps of the molecular cloud in the direction of 1E 1740.7-2942 are presented. Hydrogen column densities of the cloud vary between N(sub H) = 3.5 x 10(exp 22)/cu cm and 11 x 10(exp 22)/cu cm, depending on the method employed. From this, it is concluded that, despite the weakness of the iron fluorescent 6.4 keV line, the source may lie inside the cloud, or at least close to its edge. The combined spectra from the Advanced Satellite for Cosmology and Astrophysics (ASCA) and the burst and transient source experiment (BATSE) can be modeled with a two phase accretion disk corona model, where the hot region is detached from the cold disk. Geometrically, the hot phase can be interpreted as a number of active regions above the disk, or as a spherical hot cloud about the central object.

Vilhu, Osmi↗

NASA NTRS2000

Exploring the Extreme Universe with GLAST

The Gamma-ray Large Area Space Telescope, GLAST, is a satellite-based experiment under development to measure the cosmic gamma-ray flux in the energy range 20 MeV to > 300 GeV. With a sensitivity that is more than a factor 30 greater than that of the EGRET detector on GRO, GLAST will open a new and important window on a wide variety of high energy phenomena, including supermassive black holes and active galactic nuclei, gamma-ray bursts, supernova remnants, and searches for new phenomena such as supersymmetric dark matter annihilations and big bang particle relics. The launch is planned for 2005. This talk will include a discussion of the physics, the scientific capabilities, the novel collaboration of particle physicists and high energy astrophysicists, and the mission status.

Ritz, Steven↗

NASA NTRS1987

A gamma-ray constraint on the nature of dark matter

If even a small component of the Galactic spheroid consists of the weakly interacting majorana fermions that are cold-dark-matter candidate particles for the Galactic halo, there should be a substantial flux of annihilation gamma rays from a source of about 1-deg extent at the Galactic center. COS B observations already constrain the halo cold-dark-matter (CDM) content entrained in the inner spheroid to be less than about 10 percent. A somewhat weaker constraint applies to the CDM believed to be present in the Galactic disk, but still only about 15 percent can be in such particles. Monochromatic line photons of energy 3-10 GeV are also predicted, and future experiments may be capable of improving these limits. Since both theoretical models of galaxy formation in a CDM-dominated universe and mass models for the rotation curve in the inner Galaxy suggest that a substantial fraction of the spheroid component should be nonluminous and incorporate entrained halo CDM, the hypothesis that the halo CDM consists predominantly of weakly interacting fermions such as photinos or heavy majorana mass neutrinos or higgsinos may already be subject to observational test.

Silk, Joseph↗

NASA NTRS1992

The Crab pulsar light curve in the soft gamma ray range: FIGARO II results

The FIGARO II experiment (a large area, balloon borne, crystal scintillator detector working from 0.15 to 4.3 MeV) observed the Crab pulsar on 1990 Jul. 9 for about seven hours. The study of the pulse profile confirms some structures detected with a low significance during the shorter observation of 1986, and adds new important elements to the picture. In particular, between the two main peaks, two secondary peaks appear centered at phase values 0.1 and 0.3, in the energy range 0.38 to 0.49 MeV; in the same energy range, a spectral feature at 0.44 MeV, interpreted as a redshifted positron annihilation line, was observed during the same balloon flight in the phase interval including the second main peak and the neighboring secondary peak. If the phase interval considered is extended to include also the other secondary peak, the significance of the spectral line appears to increase.

Massaro, E.↗

NASA NTRS2021

Indirect Dark Matter Searches at Ultrahigh Energy Neutrino Detectors

High to ultrahigh energy neutrino detectors can uniquely probe the properties of dark matterχby searching for the secondary products produced through annihilation and/or decay processes. We evaluate the sensitivities to dark matter thermally averaged annihilation cross section〈σv〉and partial decay width into neutrinos Γ χ→ν ̄ν (in the mass scale 10 7 ≤ m χ /GeV ≤ 10 15 ) for next generation observatories like POEMMA and GRAND. We show that in the range 10 7 ≤ m χ /GeV ≤ 10 11 , space-based Cherenkov detectors like POEMMA have the advantage of full-sky coverage and rapid slewing, enabling an optimized dark matter observation strategy focusing on the Galactic center. We also show that ground-based radio detectors such as GRAND can achieve high sensitivities and high duty cycles in radio quiet areas. We compare the sensitivities of next generation neutrino experiments with existing constraints from IceCube and updated 90% C.L. upper limits on〈σv〉and Γ χ→ν ̄ν using results from the Pierre Auger Collaboration and ANITA. We show that in the range 10 7 ≤ m χ /GeV ≤ 10 11 POEMMA and GRAND10k will improve the neutrino sensitivity to particle dark matter by factors of 2 to 10 over existing limits, whereas GRAND200k will improve this sensitivity by two orders of magnitude. In the range 10 11 ≤ m χ /GeV ≤ 10 15 , POEMMA’s fluorescence observation mode will achieve an unprecedented sensitivity to dark matter properties. Finally, we highlight the importance of the uncertainties related to the dark matter distribution in the Galactic halo, using the latest fit and estimates of the Galactic parameters.

Particle astrophysics↗

NASA NTRS1989

Absorbing boundary conditions for second-order hyperbolic equations

A uniform approach to construct absorbing artificial boundary conditions for second-order linear hyperbolic equations is proposed. The nonlocal boundary condition is given by a pseudodifferential operator that annihilates travelling waves. It is obtained through the dispersion relation of the differential equation by requiring that the initial-boundary value problem admits the wave solutions travelling in one direction only. Local approximation of this global boundary condition yields an nth-order differential operator. It is shown that the best approximations must be in the canonical forms which can be factorized into first-order operators. These boundary conditions are perfectly absorbing for wave packets propagating at certain group velocities. A hierarchy of absorbing boundary conditions is derived for transonic small perturbation equations of unsteady flows. These examples illustrate that the absorbing boundary conditions are easy to derive, and the effectiveness is demonstrated by the numerical experiments.

Jiang, Hong↗

NASA NTRS1990

Absorbing boundary conditions for second-order hyperbolic equations

Jiang, Hong↗